The invention is based on a hydraulic adjusting device as set forth hereinafter.
German Offenlegungsschrift 41 28 656, whose publication date is not prior to the priority date of the present application, discloses one such hydraulic adjusting device, in which the partial pressures in the pressure chambers of an actuator, embodied as a differential cylinder, can be varied via an electromagnetically actuatable control valve. The partial pressures in the pressure chambers are adjusted by means of a partial outflow of pressure fluid, and by suitable triggering of the control valve, these partial pressures are kept virtually constant. Given a stationary position of the actuator, the control valve is triggered such that the holding pressures are very much less than the adjusting pressures required for an adjusting motion. To that end, the annular face of the differential cylinder is always acted upon by pressure fluid by means of a pump, while the pressure chamber on the large piston face is built up via an overflow valve and is variable by means of the electromagnetically actuatable control valve. Such a hydraulic adjusting device is used in an internal combustion engine, for instance, in order to actuate a device for adjusting the camshaft relative to the crankshaft or the drive wheel. To adjust the camshaft, the actuator and the camshaft are connected to one another via a coupling member. This coupling member is longitudinally displaceable and has a gear tooth system that cooperates with a gear tooth system on the longitudinally stationary camshaft. A further gear tooth system cooperates with a corresponding one on the drive wheel. One of these two pairs of gear tooth systems is embodied as a spur gear, while the other is embodied as a helical gear. By the cooperation of these gear tooth systems, a translational motion of the actuator is converted into a rotational motion on the part of the camshaft. Because of their design, these devices require considerable space for installation and above all have a great length axially (in the direction of the longitudinal axis of the camshaft). Moreover, such devices require at least one actively controllable valve part and at least one further, passive, not arbitrarily controllable valve part.